A water heater in the related art usually employs a stepping motor type water proportional valve, a memory alloy type water proportional valve, or a manual knob opening type regulating valve to control flow rate of inflowing water. In which, when the stepping motor type water proportional valve is employed, regulation of the flow rate of the water cannot be completed at one time due to a certain process of control, judgment and feedback, and repeated regulations are required to approach the desired flow rate of the water, a response time is prolonged, thereby causing large fluctuation of the flow rate and temperature of outflowing water. When the memory alloy type water proportional valve is employed, the flow rate of the water pulsates and is unstable during regulation due to limitation of characteristics of the memory alloy, which results in low comfort for use. When the manual knob opening type regulating valve is employed, since the opening is hard to master, the temperature of the outputting water cannot be accurate to the desired temperature.